The first vehicle safety rating systems were the US National Highway Traffic Safety Administration’s New Car Assessment Program (NCAP), started in 1979, and the Australasian NCAP, started in 1992. These systems were investigated in order to determine the methods used to develop them and the characteristics that make them scientifically valid. In addition, a proposed safety rating system for All-Terrain Vehicles (ATVs) and Side by Side Vehicles (SSVs) was compared to the automotive NCAP systems in order to determine its scientific validity. The literature related to the history and development of the original NCAP safety rating systems was reviewed. The proposed safety rating system for ATVs was also reviewed and comparisons with the original NCAP systems were made. The original NCAP systems have been based on correlations between the measured acceleration of the head and chest and actual injury outcome probabilities. These systems also were intentionally restricted to providing comparisons between vehicles of similar mass. Based on this premise, criteria for the establishment of a vehicle safety rating system have been developed with the aim to ensure that such a system has validity and provides ratings that are based on scientifically established correlations between objectively and repeatably measured values and desirable safety outcomes. The proposed safety rating system for ATVs and SSVs that was not developed following this method was found to have no basis in known relationships between the test outcomes and injury probabilities. Although the proposed safety rating system for ATVs and SSVs was found to be unacceptable, a methodology for developing a safety rating system that would meet the criteria is proposed. The methodology would involve collecting real-world injury and exposure data and correlations with measurable vehicle characteristics. This correlation could then lead to the development of scientifically valid safety rating systems for ATVs and SSVs.